Submitted on March 8, 2007
Accepted on February 21, 2008
Oxidative Stress Stimulates Skeletal Muscle Glucose Uptake Through A Phosphatidylinositol-3-kinase-dependent Pathway
Yasuki Higaki1*, Toshio Mikami2, Nobuharu Fujii3, Michael F Hirshman3, Katsuhiro Koyama4, Tetsuya Seino5, Keitaro Tanaka1, and Laurie J. Goodyear3
1 Preventive Medicine, Saga University, Saga-shi, Saga, Japan
2 Department of Health and Sports Science, Nippon Medical School, Kawasaki, Kanagawa, Japan
3 Joslin Diabetes Center, Metabolism Section, Harvard Medical School, Boston, Massachusetts, United States
4 Faculty of Education and Human Sciences, University of Yamanashi, Kofu, Yamanashi, Japan
5 Liberal Arts Division, Kisarazu National College of Technology, Kisarazu, Chiba, Japan
* To whom correspondence should be addressed. E-mail: higaki{at}cc.saga-u.ac.jp.
We determined the acute effects of oxidative stress on glucose uptake and intracellular signaling in skeletal muscle, by incubating muscles with reactive oxygen species (ROS). Xanthine oxidase (XO) is a superoxide-generating enzyme that increases ROS. Exposure of isolated rat extensor digitorum longus (EDL) muscles to hypoxanthine/XO (Hx/XO) for 20 min resulted in a dose-dependent increase in glucose uptake. To determine if the mechanism leading to Hx/XO-stimulated glucose uptake is associated with the production of hydrogen peroxide (H2O2), EDL muscles from rats were preincubated with the H2O2 scavenger catalase or the superoxide scavenger superoxide dismutase (SOD) prior to incubation with Hx/XO. Catalase treatment but not SOD completely inhibited the increase in Hx/XO-stimulated 2-DG uptake, suggesting that H2O2 is an intermediary leading to Hx/XO-stimulated glucose uptake with incubation. Direct H2O2 also resulted in a dose-dependent increase in 2-DG uptake in isolated EDL muscles, and the maximal increase was threefold over basal levels at a concentration of 600 µmol/l H2O2. H2O2-stimulated 2-DG uptake was completely inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin, but not the nitric oxide inhibitor, NG-monomethyl-L-arginine. H2O2 stimulated the phosphorylation ofAkt Ser473 (7-fold) and Thr308 (2-fold) in isolated EDL muscles. H2O2 at 600 µmol/l had no effect on ATP concentrations and did not increase the activities of either the 
1 or 2 catalytic isoforms of AMP-activated protein kinase. These results demonstrate that acute exposure of muscle to ROS is a potent stimulator of skeletal muscle glucose uptake and that this occurs through a PI3K-dependent mechanism.
